Cutting back coleus will actually produce more of it, making the plant take on a bushier shape quite quickly. The flowers are often pinched from coleus plants so the leaves aren’t downplayed, but doing so also makes this tender perennial (often grown as a summer annual in cold climates) fuller by keeping the height under control and creating the opportunity for more leaves to grow.
To pinch back your coleus, simply cut or pinch off any stem at a point where two stems or two leaves are growing from it. Two new branches will begin to grow from where those other stems or leaves meet the main stem that you pinched.
You can also pinch just under the coleus’s flower buds if you don’t want the plant’s energy to be spent on producing flowers and seeds. (When this happens, the leaves lose beauty and vigor.) Around midsummer, coleus should be pruned regardless of whether it will be allowed to flower. If it’s not maintained, it could overgrow and branches can snap from their weight.